In residential as well as industrial construction the structure is commonly enclosed by means of two brick walls placed at a certain distance from one another forming an air space. The space between the two walls is filled with an insulating material. This procedure involves very high labor costs in the construction of the two parallel walls a certain distance apart, as well as very high costs for the necessary insulating material. Moreover, the insulating material sublimes over time, that is it becomes depleted, reducing the function of the air space until it is eliminated, and with it the function of providing good insulation.
It is known that to reduce the weight and improve the insulation of a construction brick, the raw material mixture, for exmple of clay, is treated with combustible organic materials like sawdust, peat, cork, coal dust and the like. When the bricks are fired, these materials are released in gaseous form giving rise inside the brick to an alveolar configuration which has the due effect of improving insulation and lightening the brick. However, these combustible organic materials cannot be added to the mixture beyond a certain degree since increasing the quantity considerably decreases the moldability of the mixture due to the relatively high friction of said materials. Furthermore, increasing the quantity of organic material incorporated, greatly lowers the pressure resistance since the incorporated material impedes the natural contraction of the raw material during drying. This leads to cracks which propagate because of the above mentioned friction of the incorporated material. Thus, increasing the quantity of material placed in the mixture widens the cracks so much the strength of the product is seriously reduced.
In order to overcome these problems and obtain a porous, insulating and light, but high strength brick or block, Italian Pat. No. 605,312 proposes incorporating in the raw material (clay, kaolin, clay schists and the like) a compressible material synthetic in nature, molding the resulting mixture to form the final product, drying it, and finally firing it. Since the incorporated material can be compressed to a smaller volume, it does not prevent contraction of the raw material during drying. Crack formation is thus substantially reduced or even eliminated, and the compression strength of the product is not compromised. The systhetic compressible material is placed in the mixture in the form of pieces made to swell or foam, preferably in the form of small beads. For the material to be incorporated, Italian Pat. No. 605,312 proposes a synthetic material like polystyrene, phenol-plastics, polyvinyl synthetics like polyvinyl chloride, or polyesters, formaldehyde urea, polyurethane, polyethylene, polyisobutylene, latex rubber, silica and cellulose derivatives like cellulose acetate.
A brick as described has been marked under the name "Poroton". It is rectangular in shape and subdivided by means of partitions, running along its width into several chambers parallel to one another and connected by several partitions orthogonal to the former, so as to form an actual lattice. The periphery of the brick, like all its partition, has an alveolar structure, as described below, in order to reduce weight and allow good insulation. Such a brick responds in effect, both in terms of cell-like structure and of the percent of openings (maximum 45%), that is of the empty spaces created in the chambers formed by the partitions and the cell-like structure, to the properties listed for bricks prepared with cell-like structure using compressible organic materials. However, it should be noted that the insulation is a function only of the cell-like structure and that to obtain said structure, one must use synthetic compressible material whose cost is not negligible. On the other hand, the quantity of said material may not, even in this type of brick, exceed a certain amount, to prevent excessive weakening of the brick itself.
In this regard, it should be noted that heat is transferred by radiation, convenction and conduction. Transmission by radiation is considered to be negligible, and so it will not be considered. Transmission by air convection occurs vertically toward the ceiling; the quantity of heat which the air can transmit horizontally toward the outside, or vice versa, is negligible when the chambers are developed vertically, with as little horizontal development as possible. Transmission by conduction occurs through solid bodies (clay, in the present case) horizontally. Therefore, the insulation of a brick is enhanced by reducing the possibility of heat diffusion by conduction to a minimum. In the brick in question, however, the various chambers are connected to one another, from the inside toward the outside, by several septa which form several actual heat bridges, which facilitate heat transmission by conduction in this direction with a result of cancelling the effect of the chamber presence, and reducing the insulating effect which could have been achieved by the cell-like structure.
The insulating effect of the latter structure however is a function of the greater or lesser regularity of the mixing of the additive with the clay. This obviously leads to the manufacture of bricks with different insulating capacities. The aim of this invention is thus to overcome the inconveniences mentioned above by proposing a lightweight but still very strong brick, with low production costs and, above all, enhanced insulation.